1. Field of the Invention
The present invention relates to boating, and more specifically to a variable area trim tab system and method to control water flow along a trim tab and added propeller guard including tunnel propellers.
2. Description of the Related Art
Trim tabs are historically used to control the flight attitude of a boat by changing the localized slope of a portion of the bottom surface of the boat. Prior art trim tabs may be attached to the boat hull by hinges or solidly affixed and may either be held rigid or be made to flex by control means. Existing trim tabs are not configured to be controlled to allow increased water flow to the propeller. Existing trim tabs that are located in front of, and below, the propeller are used to limit variations of propeller blade immersion. Existing trim tabs are known which have flow limiting flood walls or flood curtains to decrease the flow of water to the propeller. Such existing trim tabs do not have means to increase the flow of water to the propeller.
Adding trim tabs to a boat changes the overall wetted area footprint of a bottom of the boat and thus will usually change the flight attitude of the boat. Boats with a propeller in a tunnel may have a fixed geometry closure panel as a continuation of the boat's bottom surface. For example, U.S. Pat. No. 6,464,549 to Buzzi (Buzzi '549) refers to the closure panel as a “ground wall”, but it is in a fixed position and has only one opening and that is located where the propeller shaft emerges from the rearward end of a tunnel near the propeller. Buzzi '549 describes the tunnel as having only a single opening and is not classified as a trim tab but instead as means to control flow around a propeller. The mere presence of Buzzi's closure in contact with the flowing water, however, changes the wetted footprint of the bottom of a boat. Although the area of Buzzi's closure may be small and its contribution to the flight attitude may be small, it still exists and has the flavor of a trim tab. U.S. Pat. No. 4,909,175 to Arnseson (Arnseson '175) shows a flexing trim tab attached to the boat bottom forward of the stern. Prior art trim tabs do not include a propeller guard to protect the propeller from being damaged or propeller screens to protect swimmers or marine mammals.